I was just trying to find out where I could purchase a intercom/buzzer system for a small apartment building. I am looking at a 16 unit building and would like to install one of these systems if I purchase. The kind that will unlock the main door to let guests in if the tennant “buzzes them in”. I have googled it already and so far cannot find what I am looking for but will keep searching. I know it might be a little early looking for something like this but I am curious about the cost.
Thanks,
Jon
Found some info but recomendations on what anyone has used would be nice! 
Thanks,
Jon
A better idea might be the one that works off the phone system.
They dial up the tenant via land line and the tenant can buzz them in by pressing a number on the phone. No wiring to each apartment. Just phone line and door striker/latch. New tenants can be programmed remotely by you dialing in.
A modest system can be had for a very reasonable price.
A good rule would be not to program entry numbers to people’s cell phones. It must be a home phone. That way they can’t let people in form 100 miles away. Get a copy of local phone bill with their address for proof.
google “telephone entry systems” There are dozens of them out there.
I used to be an intercom/security system/security gate installer. There are basically two types of systems. One requires each unit to be hard wired to a central system, which for an existing building is expensive and sometimes impossible. The most common type of this system is Aiphone.
The second type is what JeffinCT taked about. You have a system that runs on it’s own phone line (this is important) and power. You program all the tenant phone numbers and access codes in (via computer modem or manually) and install an electric door strike or mag lock. Mag locks are easier to install, but a bit more expensive than an electric strike. The person calls from the box and the tenant pushes 9 on their phone to grant access, or hangs up to deny access. NOT programming cell phones in can be a bad idea, it just depends on the tenants. Some people, like myself, only have cell phones, and if I’m in New York, and I want to let the UPS man in to leave a package, I can. Or I can always choose not to let anyone in.
A few of the major companies with a telephone type system are Elite Access, DoorKing, Sentex Systems and Keri Systems. I have installed and worked on all of these, and all have MANY capabilities like card readers, remote controls, time clocks for automatic lock/unlock and a whole bunch of crap you’ll never use. The most important thing is to make sure you educate your tenants on how to use it, and change the access codes every quarter.
I guess I really didn’t answer your question. Sorry about that. There are a few places from which you can purchse online, I will get the names and numbers later today from suppliers I used to purchase from.
If you have little experience in installing one of these, I would recommend hiring a pro. Some of these systems are pretty complicated and easy to screw up. I’ll get you that info here shortly.